For internal combustion engines, such as diesel engines, nitrogen oxide (NOx) compounds may be emitted in the exhaust. To reduce NOx emissions, a selective catalytic reduction (SCR) process may be implemented to convert the NOx compounds into more neutral compounds, such as diatomic nitrogen, water, or carbon dioxide, with the aid of a catalyst and a reductant. The catalyst may be included in a catalyst reaction tube of an exhaust system, such as that of a vehicle or power generation unit. A reductant such as anhydrous ammonia, aqueous ammonia, or urea is typically introduced into the exhaust gas flow prior to the catalyst reaction tube. To introduce the reductant into the exhaust gas flow for the SCR process, an SCR system may dose or otherwise introduce the reductant through a doser that vaporizes or sprays the reductant into an exhaust pipe of the exhaust system up-stream of the catalyst reaction tube. The SCR system may include one or more sensors to monitor conditions within the exhaust system.